Method and device for transmitting signals in a wireless communication system, receiving device for receiving signals in a wireless communication system, with a special frame structure

ABSTRACT

The present invention relates to a method for transmitting signals in a wireless communication system, in which signals are transmitted from a first communication device to a second communication device, said signals being transmitted in consecutive frames, each frame having a preamble section including preamble information, at least one of said first and said second communication devices having a narrow beam antenna which is adapted to be steered to different positions, each of said different positions corresponding to one of a number of different transmissions paths from said to said second communication device, including the steps of transmitting and receiving a first preamble section including preamble information enabling the estimation of a channel quality of a current transmission path, while said narrow beam antenna is in a current position corresponding to said current transmission path, steering said narrow beam antenna from said current position to a different position corresponding to a candidate transmission path, and transmitting and receiving a second preamble section including preamble information enabling the estimation of a channel quality of said candidate transmission path while said narrow beam antenna is in said different position. The present invention further relates to a corresponding transmission device as well as a receiving device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of and claims the benefit priorityfrom U.S. Ser. No. 11/853,403, filed Sep. 11, 2007, the entire contentsof which are incorporated herein by reference. U.S. Ser. No. 11/853,403claims the benefit of priority from European Application No. 06 021151.3, filed Oct. 9, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and a device for transmittingsignals in a wireless communication system, as well as to a receivingdevice for receiving signals in a wireless communication system with aspecial frame structure enabling a high data rate transmission andreception with at least one steerable narrow beam (sharp beam) antenna.

2. Discussion of the Background

Wireless communication is used in a large variety of technical fields,such as mobile telephone, wireless LAN, walky-talkies, broadcast radiosystems, point-to-point radio systems and many other known and futureapplications. The communication radius covered by a respective wirelesscommunication system basically depends on the technique used. Whereascellular communication systems, such as the GSM and the UMTS system, areadapted for a communication radius up to about 10 km (or more), wirelessLAN is in the range of about 100 m (or more) and the Bluetooth system isin the range of several 10 m (or more). The major influences on thecommunication range of a wireless communication system are the radiofrequency and output power used. Although only little absorption ofelectromagnetic waves in the atmosphere occurs at the radio frequencyused for GSM and UMTS, a significant absorption occurs in the 60 GHzrange, which makes it quite well suited for low range and indoorwireless communication. Furthermore, the kind of transmission and/orreception antennas used for a respective wireless communicationtechnique varies depending on a respective field of application. Forexample, if a number of receivers has to be reached or if the locationof the receivers is unknown or varies frequently, e.g. due to movement,wide beam antennas or omni-directional antennas are sometimes used.However, the utilization of wide beam antennas in high data ratemillimeter wave wireless communication systems is problematic, becauseof the multi-path fading effect. For example, if wide beam antennas areused both on the transmitter and the receiver side and if the directline of sight (LOS) link is blocked by an obstacle, such as a movinghuman being, a vehicle or the like, there exist a lot of reflectionpaths between the transmitter and the receiver, i.e. transmission pathsin which the transmitted electromagnetic wave is reflected at least onceby objects before it reaches the receiver. The channel delay spreadmight be over tens of symbol periods when the data rate is high, e.g.over 1 Gbps, which leads to severe inter-symbol interference due to deepfrequency selective fading.

Two conventional solutions exist for such kind of non line of sight(NLOS) user scenarios, whereby both of these solutions need high-speedand complex signal processing circuits. One solution adopts a channelequalizer including linear, decision feedback or maximum likelihoodsequence estimation (MLSE) equalizer. When the channel delay spread ismuch longer than the symbol duration, the equalizer becomes complex andneeds a lot of processing power. Another solution is the orthogonalfrequency division multiplexing (OFDM) technique, which is alreadyadopted in wireless LAN systems. However, due to its inherent linearmodulation and high peak to average ratio problems, the powerconsumption of the power amplifier (PA) in such systems is very high.Obviously, a high speed Fast Fourier Transformation and other signalprocessing modules are required for demodulating a 1 Gbps signal.Therefore, it is important to find other solutions which do not requirecomplex and high speed base band circuitry for high data rate millimeterwave range communication systems.

SUMMARY OF THE INVENTION

The above objections are achieved by a method for transmitting signalsin a wireless communication system according to claim 1, a transmittingdevice for transmitting signals in a wireless communication systemaccording to claim 9 and a receiving device for receiving signals in awireless communication system according to claim 17.

According to the present invention, a method for transmitting signals ina wireless communication system, in which signals are transmitted from afirst communication device to a second communication device, saidsignals being transmitted in consecutive frames, each frame having apreamble section comprising preamble information, at least one of saidfirst and said second communication devices having a narrow beam antennawhich is adapted to be steered to different positions, each of saiddifferent positions corresponding to one of a number of differenttransmission paths from said first to said second communication device,comprises the steps of transmitting and receiving a first preamblesection comprising preamble information enabling the estimation of achannel quality of a current transmission paths, while said narrow beamantenna is in a current position corresponding to said currenttransmission path, steering said narrow beam antenna from said currentposition to a different position corresponding to a candidatetransmission path, and transmitting and receiving a second preamblesection comprising preamble information enabling the estimation of achannel quality of said candidate transmission path while said narrowbeam antenna is in said different position.

Advantageously, at least some of said frames comprise a first and asecond preamble section. Further advantageously, every frame comprises afirst and a second preamble section. This means that a first and asecond preamble section are contained in each frame. In an alternativeembodiment, the first and the second preamble section are advantageouslytransmitted in different frames. Hereby, the number of transmittedframes comprising a second preamble section in relation to the number oftransmitted frames comprising a first preamble section is varieddepending on a detected channel quality for the current transmissionpath. Further advantageously, the number of transmitted framescomprising a second preamble section in relation to the number oftransmitted frames comprising a first preamble section is varieddepending on a detected movement information in relation to the firstand/or the second communication device. Further advantageously, aftereach frame comprising a second preamble section a frame comprising afirst preamble section with a longer length as compared to the normallytransmitted frames comprising a first preamble section is transmitted.Further advantageously, the first and the second preamble sections aredifferent from each other.

According to the present invention, a transmitting device fortransmitting signals in a wireless communication system, wherein saidsignals are transmitted in consecutive frames, each frame having apreamble section with preamble information, comprises a narrow beamantenna adapted to be steered to different positions, each of saiddifferent positions corresponding to one of a number of differenttransmission paths from said transmitting device to a receiving device,a steering means adapted to steer said antenna to different positions,preamble generating means adapted to generate preamble sectionscomprising preamble information, control means adapted to control thetransmission of a first preamble section comprising preamble informationenabling the estimation of a channel quality of a current transmissionpath while said narrow beam antenna is in a current positioncorresponding to said current transmission path, and further adapted tocontrol the transmission of a second preamble section comprisingpreamble information enabling the estimation of a channel quality of acandidate transmission path after said narrow beam antenna has beensteered to a different position corresponding to said candidatetransmission path.

Advantageously, the control means is adapted to control the transmissionof at least some frames comprising a first and a second preamblesection. Further advantageously, the control means is adapted to controlthe transmission of signals in which every frame comprises a first and asecond preamble section. In an alternative embodiment, the control meansis adapted to control the transmission of signals in which said firstand said second preamble section are transmitted in different frames.Hereby, the control means is advantageously adapted to vary the numberof frames comprising a second preamble section in relation to the numberof frames comprising a first preamble section depending on a detectedchannel quality for the current transmission path. Furtheradvantageously, the control means is adapted to vary the number oftransmitted frames comprising a second preamble section in relation tothe number of transmitted frames comprising a first preamble sectiondepending on a detected movement information in relation to thetransmission and/or the receiving device. Hereby, the control means isadvantageously adapted to control the transmission of signals so thatafter each frame comprising a second preamble section a frame comprisinga first preamble section with a longer length as compared to thenormally transmitted frames comprising a first preamble section istransmitted. Advantageously, the first and the second preamble sectionsare different from each other.

According to the present invention, a receiving device for receivingsignals in a wireless communication system, wherein said signals aretransmitted and received in consecutive frames, each frame having apreamble section with preamble information, comprises a narrow beamantenna adapted to be steered to different positions, each of saiddifferent positions corresponding to one of a number of differenttransmission paths from a transmitting device to a receiving device, asteering means adapted to steer said antenna to different positions,channel estimation means adapted to estimate a channel quality on thebasis of received preamble information, control means adapted to controlthe reception of a first preamble section comprising preambleinformation enabling the estimation of a channel quality of a currenttransmission path while said narrow beam antenna is in a currentposition corresponding to said current transmission path, and furtheradapted to control the reception of a second preamble section comprisingpreamble information enabling the estimation of a channel quality of acandidate transmission path after said narrow beam antenna has beensteered to a different position corresponding to said candidatetransmission path.

Advantageously, the control means is adapted to control the reception ofat least some frames comprising a first and a second preamble section,hereby, the control means is advantageously adapted to control thereception of signals in which every frame comprises a first and a secondpreamble section. In an alternative embodiment, the control means isadvantageously adapted to control the reception of signals in which saidfirst and said second preamble section are transmitted in differentframes. Hereby, the control means is advantageously adapted to controlthe reception of signals in which the number of frames comprising asecond preamble section in relation to the number of frames comprising afirst preamble section is varied depending on the detected channelquality for the current transmission path. Hereby, the control means isadvantageously adapted to control the reception of signals in which thenumber of transmitted frames comprising a second preamble section inrelation to the number of transmitted frames comprising a first preamblesection is varied depending on a detected movement information inrelation to the first and/or the second communication device. Thecontrol means is further advantageously adapted to control the receptionof signals so that after each frame comprising a second preamble sectiona frame comprising a first preamble section with a longer length ascompared to the normally transmitted frames comprising a first preamblesection is received. Further, the control means is advantageouslyadapted to control the reception of first and second preamble sectionswhich are different from each other.

The present invention therefore provides a solution for a high data ratewireless communication in the millimeter wave length range which doesnot require a complex and high-speed processing. Specifically, when thetransmission data rate becomes high, e.g. in the range of 1 Gbps orbeyond, the frame length should be shortened in order to keep theperformance of the frame error rate (FER) under the same bit error rate(BER). When the frame length becomes shorter, the overhead, i.e. thepreamble information, necessary for the beam steering algorithm ishigher. The present invention enables to reduce this overhead bydefining a new frame structure including the definition of differenttypes of frames, and how to combine these new types of frames togetherto enable both a wireless data communication with a high data rate and anarrow beam antenna steering. The specific advantages of the presentinvention are that the additional overhead for the beam steering is low,the frame length can be shortened for high data wireless communicationsystems in order to improve the performance of the frame error rateunder the same bit error rate, and the speed of the beam steering can bedynamically changed and increased.

It is to be noted that the present invention can be applied to any kindof wireless communication system which enables the transmission andreception of signals over any kind of range. Further, the presentinvention is not restricted to any kind of modulation schemes ortechnical implementation of the wireless communication. Some embodimentsand implementations of the present invention, however, might beadvantageous in short and/or mid range wireless communication systems inwhich signals are transmitted in the millimeter wave range, as e.g. the60 Ghz transmission range. Further, the transmitting device and thereceiving device of the present invention can be any kind of deviceadapted to transmit and receive, respectively, signals in a wirelesscommunication system. The terms ‘transmitting device’ and ‘receivingdevice’ are hereby intended to comprise any kind of portable and/orstationary communication equipment, unit, means, system and so forth.The signals to be transmitted from the transmitting device to thereceiving device according to the present invention may comprise anykind of information, data, symbols and so forth which can be transmittedfrom a transmitter to a receiver for any kind of reason and utility.According to the present invention, at least one of the transmittingdevice and the receiving device comprise a narrow beam antenna which isadapted to be steered to different positions. In some implementations itmight be preferable that the transmitting device and the receivingdevice each comprise a narrow beam antenna which is adapted to besteered to different positions. The term ‘narrow beam antenna’ is herebyintended to comprise and cover all kinds of antennas which, in contraryto omni-directional antennas which do not have a specific transmissionand/or reception direction, have a specific transmission and/orreception direction without any limitation to the specific shape of theantenna beam. Further, the narrow beam antenna of the present inventionis not restricted to any specific steering type, i. e. the specifictechnical implementation which enables the steering or switching of thenarrow beam antenna to different transmitting and/or reception positionsas long as the transmitting and/or receiving direction of the narrowbeam antenna can be changed, switched, varied and the like. For example,but not exclusively, a narrow beam antenna according to the presentinvention may be an antenna with a fixed narrow beam radiation pattern,which can be varied by mechanically or electrically shifting the antennaso that the beam direction is varied. Further, the narrow beam antennacould be an antenna type which can be steered by changing the phaseand/or the gain of the antenna so that the beam direction changes. As afurther alternative, the narrow beam antenna could consist of an antennapattern, whereby each of the antenna elements of the antenna pattern hasa specific narrow beam antenna direction and the elements can becontrolled in a way that the beam direction of the antenna is changed.Many other examples of steerable narrow beam antennas can be made, whichare currently known or which may be developed in the future, but whichwould fall under the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be explained in more detail in the followingdescription of preferred embodiments in relation to the encloseddrawings, in which

FIG. 1 schematically shows a transmitting device according to thepresent invention,

FIG. 2 schematically shows a receiving device according to the presentinvention,

FIG. 3 schematically shows a variety of transmission paths between atransmitter and a receiver,

FIG. 4 schematically shows a first embodiment of a frame according tothe present invention,

FIG. 5 schematically shows a second embodiment of frames according tothe present invention,

FIG. 6 schematically shows the implementation of the second embodimentin consecutive frames,

FIG. 7 schematically shows the implementation of the second embodimentin a consecutive number of frames,

FIG. 8 schematically shows a further variation of frames within thesecond embodiment, and

FIG. 9 schematically shows the implementation of the frames of FIG. 8 ina number of consecutive frames.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a schematic block diagram of a transmitting device fortransmitting signals in a wireless communication system according to thepresent invention. Hereby, the transmitting device 1 of the presentinvention as shown in FIG. 1 is only displayed with elements which arenecessary for the implementation and the understanding of the presentinvention. All other necessary elements enabling the transmitting device1 to transmit signals in a wireless communication system are not shownfor the sake of clarity. However, in a practical implementation, allsuch elements would be implemented.

The transmitting device 1 comprises a narrow beam antenna 2 which isadapted to be steered to different positions under the control of anantenna steering means 4, which itself is controlled by a control means5. The control means 5 can be a baseband processing and/or controllingmeans of the transmitting device 1 or any other suitable control unit.The control means 5 is connected to a memory 6 for storing data,information, applications, software code and so forth.

The transmitting device 1 is adapted to transmit signals in consecutivetime frames, whereby each frame has a preamble section comprisingpreamble information. Examples of such frames are shown in FIGS. 4, 5and 8. Examples for a number of consecutive time frames transmitted bythe transmitting device 1 are shown in FIGS. 6, 7 and 9. Hereby, it isto be understood that the term ‘consecutive’ does not necessarily meanthat the frames are transmitted immediately one after the other. In someimplementations there might be an interval Tg between two consecutiveframes, which e. g. can be used to handle the clock difference between atransmitting device 1 and a receiving side, such as the receiving device10 as shown and explained in FIG. 2, in order to support long time andhigh rate wireless communications, such as wireless high definitiontelevision or the like. In the following description and explanations,the interval Tg between two consecutive time frames is assumed to bezero. In a first embodiment of the frame structure according to thepresent invention which is shown in FIG. 4, a frame, such as frame shownin FIG. 4 having a length of Tf, comprises a preamble section and a datasection. The preamble section is generated by a preamble sectiongenerator 9 of the transmitting device 1, whereby the preamblegeneration can either take place in the frequency domain or the timedomain processing. Further, the preambles generated by the preamblesection generator 9 can have different lengths and sizes depending onthe wanted implementation. The frames are formed by a frame generator 7which obtains the preamble sections from the preamble section generator9 and the data from the data means 8. The data means 8 generates,collects, or obtains the data in any kind of suitable way and forwardsthe data to the frame generator 7. After a frame has been generated bythe frame generator 7, the generated frames are then further processedin the usual manner, e. g. by modulating the frame information or thelike, which are then up-converted and transmitted via a high frequencymeans 3 through the narrow beam antenna 2.

The preamble section of the frames of the first embodiment as shown inFIG. 4 comprises essentially four parts, namely a training sequence Trfor aligning the direction of narrow beam antenna to candidatetransmission paths, time and frequency synchronization, a preamblesequence Pr enabling the estimation of channel quality information in areceiver for that candidate path, a training sequence Tc for aligningthe direction of narrow beam antenna to a currently used transmissionpath, time and frequency synchronization, and a preamble sequence Pcenabling the estimation of channel quality information in a receivingdevice for the currently used transmission path as well as the frametiming in the receiving device.

An example of a receiving device 10 for receiving signals in a wirelesscommunication system according to the present invention is schematicallyshown in the block diagram of FIG. 2. The receiving device 10 comprisesa narrow beam antenna 11 which is adapted to be steered to differentpositions by an antenna steering means 13 under the control of a controlmeans 14. The control means 14 can be any kind of suitable controlmeans, such as a baseband processing means of the receiving device 10,or any other suitable control and/or processing device. The controlmeans 14 is connected to a memory means 15 adapted to store data,information, applications, software programs and so forth necessary forthe operation of the receiving device 10. The receiving device 10further comprises a high frequency section 12 which is used todownconvert the received signals via the antenna 11, which are thenfurther processed in the usual manner in the receiving device 10. Forexample, a channel estimator 16 is adapted to perform a channelestimation on the basis of received preamble information. The channelestimation information derived by the channel estimator 16 can e. g. beused in the control means 14 for steering the antenna 11 to a suitableposition via the antenna steering means 13. It is to be noted that FIG.2 only shows the necessary elements for understanding the presentinvention. In a practical implementation the receiving device 10 wouldcomprise all other necessary elements for the operation of the receivingdevice 10 enabling the reception of signals in a wireless communicationsystem. Further, it is to be noted that the receiving device 10 canadditionally comprise all necessary elements and functionalities totransmit signals in the wireless communication system either via theantenna 11 or a separate transmission antenna. Likewise, thetransmitting device 1 could comprise all necessary elements andfunctionalities enabling the reception of signals in the wirelesscommunication system either via the antenna 2 or a separate receptionantenna. Further, the elements and functionalities of the transmittingdevice 1 shown and explained in relation to FIG. 1 and of the receivingdevice 10 shown and explained in relation to FIG. 2 could be combined ina communication device 1 enabling the transmission and reception ofsignals in the wireless communication system.

FIG. 3 shows a schematic diagram of various transmission paths between anarrow beam antenna 2′ of a transmitting device and a narrow beamantenna 11′ of a receiving device. The transmitting narrow beam antenna2′ might be the antenna 2 of the transmitting device 1 shown in FIG. 1and the receiving narrow beam antenna 11′ might be the antenna 11 of thereceiving device 10 of FIG. 2. However, it is to be understood that thepresent invention could also function if only the transmitting device orthe receiving device has a steerable narrow beam antenna and the otherdevice only has a wide beam or omni-directional antenna. As shown inFIG. 3, a current transmission path P₀ is not a direct line of sighttransmission path, but is a transmission path in which theelectromagnetic signals are reflected once by an object. The direct lineof sight transmission path between antenna 2′ and antenna 11′ is blockedby an obstacle 17. Candidate transmission paths, i. e. alternativepossible transmission paths between the antenna 2′ and the antenna 11′are shown as transmission paths P₁, P₂, P₃ and P₄. The candidatetransmission paths P₁, P₃ and P₄ are transmission paths in which theelectromagnet signals are reflected once by an object. The candidatetransmission path P₂ is a candidate transmission path in which theelectromagnetic signals are reflected twice on objects. However, allreflections of the candidate transmission paths are in a way that thereflected electromagnetic signal reaches the receiving antenna 11′.However, in the example shown in FIG. 3, the currently used transmissionpath P₀ has the best channel properties, e.g. the strongest signal tonoise ratio or any other suitable parameter, and is therefore currentlyused for transmitting frames between the transmitter and the receiver.The candidate transmission paths P₁, P₂, P₃ and P₄ are shown with brokenlines indicating that the channel qualities of these candidatetransmission paths are not as good as the one of the currently usedtransmission path P₀. However, in case that the channel qualities of thecurrently used transmission path P₀ changes, e. g. if the reflectionobject moves or if the transmission path is blocked by another object orobstacle due to movement or the like, one of the candidate transmissionpaths P₁, P₂, P₃ and P₄ might become the current transmission path.

Generally, FIG. 3 also visualizes that usually only a quite low numberof transmission paths provide a transmission quality which enables thetransmission and reception of signals between a transmitter and areceiver. In order to find and monitor all sufficiently strongtransmission paths, it is necessary to search and monitor all availableand possible transmission paths, whereby the transmitting narrow beamantenna 2′ and the receiving narrow beam antenna 11′ have a lot oftwo-dimensional choices. For example, if the scanning range is 100degrees and the half power beam width (HPBW) of the sharp beam steeringantenna is 20 degrees, then the number of choices from each side is5×5=25 and the total number of choices for both the transmission and thereceiving side is 25×25=625. The resulting calculation complexity isvery high.

The present invention now suggests a very simple but elegant andeffective way to transmit frames on a current transmission path whilemonitoring and checking candidate transmission paths from time to timein order to be able to switch to a different transmission path if thecurrently used transmission path deteriorates. Further, the presentinvention suggests a new frame structure which reduces the overhead forthe measurement of the channel quality and enables the implementation ofa fast beam steering algorithm.

As stated above, the first embodiment of the frame structure of thepresent invention shown in FIG. 4 suggests a frame with a structure asdescribed above. During the training sequence Tr, the control means 5 ofthe transmitting device 1 causes the antenna steering means 4 to steerthe antenna 2 from the position which corresponds to the currently usedtransmission path to a position which corresponds to a candidatetransmission path. At the same time, the control means 14 of thereceiving device 10 causes the antenna steering means 13 to steer theantenna 11 to a position which corresponds to the same candidatetransmission path so that the training sequence Tr as well as thepreamble sequence Pr can be received while the antenna 11 is in thedifferent position corresponding to the candidate transmission path. Thetraining sequence Tr enables the synchronization of the receiving device10 to the transmitting device 1 over the candidate transmission path, e.g. for timing or carrier recovery, whereas the preamble sequence Prenables the channel estimator 16 to estimate the channel qualityinformation of the candidate transmission path. After transmission ofthe preamble sequence Pr, the antenna 2 of the transmitting device 1 isswitched back to the position corresponding to the currently usedtransmission path. After receipt of the preamble sequence Pr, theantenna 11 is switched back to the position which corresponds to thecurrently transmission path. Thereafter, the training sequence Tc forthe currently used transmission path is transmitted from thetransmitting device 1 to the receiving device 11 and enablingsynchronization, i. e. timing or carrier recovery, for the currentlyused transmission path in the receiving device 10. Afterwards, thepreamble sequence Pc is transmitted from the transmitting device 1 tothe receiving device 10 enabling the estimation of accurate channelquality information by the channel estimator 16 in the receiving device10, as well as enabling the frame timing in the receiving device 10.

It has to be understood, and that is true for all embodiments of thepresent invention explained herein that the transmitting device 1 andthe receiving device 10 have to have knowledge about the respectivelynext candidate transmission path to be used in case that both thetransmitting device 1 and the receiving device 10 comprise a steerablenarrow beam antenna. In case that only one of the transmitting device 1and the receiving device 10 comprise a steerable narrow beam antenna,such previous knowledge is not absolutely necessary, but might benecessary in order to give the transmitting device 1 some feedback aboutwhich candidate transmission channel has which channel qualities.Hereby, the corresponding information could e. g. be stored in thememory means 15 of the receiving device 10 and/or the memory means 6 ofthe transmitting device 1, so that in case that the current transmissionchannel breaks down, the candidate transmission channel which had thebest channel quality is chosen to become the current transmissionchannel and the antennas 2 and 11 are steered to the correspondingpositions.

In case that the data rate should become higher, e. g. in the range of 1Gbps, the frame length Tf or the length of the data part of the framemust be shortened as compared to the frame length Tf of the firstembodiment shown in FIG. 4 in order to improve the performance of theframe error rate. For example, if the bit error rate is equal to 1×10⁻⁷,if the data rate is 1 Gps, if it is assumed that the length of the datapart is 10 ms and if a random error is assumed, since the number of datain each frame is 1×10⁷ (10 ms multiplied with data rate of 1 Gpbs), theperformance of the frame error rate is very bad. However, if e. g. thelength of the data part is reduced from 10 ms to 100 μs, the number thedata in each frame is 1×10⁵, so that the frame error rate becomes betterthan 1 percent. Since the length of the training sequence Tr and thepreamble sequence Pr are fixed, since they only depend on real circuits,in case that the length of the data part is reduced in each frame, therelative overhead introduced by Tr+Pr in relation to the data partbecomes very high. For example, when the length of a data part in aframe is changed from 10 ms to 100 μs, the overhead increases by about100 times. In order to solve this problem, a new physical framestructure according to the second embodiment as shown in FIG. 5 issuggested, which comprises two different types of physical layer frames,namely a data frame comprising a preamble section with a trainingsequence Tc and a preamble sequence Pc and a data section, as well as abeam steering frame only comprising a training sequence Tr and apreamble sequence Pr are suggested. The training sequences Tr and Tc areidentical in their features and functions as the corresponding trainingsequences Tr and Tc, respectively, shown and explained in relation toFIG. 4. The same is true is for the preamble sequences Pr and Pc, whichare identical in features and functions as the corresponding preamblesequences Pr and Pc, respectively, shown and explained in relation toFIG. 4.

As a result, by introducing the separate beam steering frames, whichonly and exclusively comprise the training sequence Tr and the preamblesequence Pr, the fixed speed of the beam steering algorithm does noteffect a frame error rate for the data frames. As schematicallyillustrated in FIG. 6, the data frames of the second embodiment can betransmitted more frequently than the beam steering frames, so that theoverhead introduced by the beam steering frames can be reduced. Forexample, the beam steering frame could be transmitted and received aftera certain number of data frames during a regular transmission. However,in case that the channel quality of the currently used transmission pathas estimated in the channel estimator 16 of the receiving device 10deteriorates, the frequency of the beam steering frames can be increasedin order to quickly find candidate transmission paths with a betterchannel quality. In other words, the number of beam steering frameswhich are transmitted from the transmitting device 1 to the receivingdevice 10 can be adapted depending on the channel quality estimated inthe receiving device for the currently used transmitting path. In casethat the channel quality of the currently used transmitting pathdeteriorates, the number of the beam steering frames is increased.Alternatively or additionally, the frequency of the beam steering framesin relation to the data frames can be dynamically adjusted based onadditional features and/or parameters of the transmitting device 1and/or the receiving device 10, e. g. the movement of one of thedevices, such as the acceleration, rotation and so forth, or any othersuitable parameter. An example for an increased frequency of thetransmission of beam steering frames is schematically shown in FIG. 7.

As shown in FIG. 8, the data frame of the second embodiment as shown andexplained in relation to FIG. 5 can comprise two types, namely a longdata frame and a short data frame. As shown in FIG. 9, according to thepresent invention, it is suggested that a long data frame should betransmitted and received immediately after a beam steering frame hasbeen transmitted and received. The other data frames are short dataframes. Hereby, a long data frame comprises a preamble section with atraining sequence Tc(L) and a preamble sequence Pc(L), and a datasection. The training sequence Tc(L) is a training sequence for thecurrently used transmission path and has the function to enable theswitching of the antennas 2 and 11 (and/or further circuitry) from theposition corresponding to the candidate transmission path of theimmediately preceding beam steering frame back to the positioncorresponding to the currently used transmission path, and then toenable synchronization, i. e. timing or carrier recovery, for thecurrently used transmission path in the receiving device 10. Thepreamble sequence Pc(L) has the function to enable the estimation ofaccurate channel quality information in the channel estimator 16 of thereceiving device 10 for the currently used transmission path as well asthe realization of frame timing in the receiving device 10. The trainingsequence Tc(S) of the short data frame only has the function to enablethe synchronization, i. e. timing or carrier recovery, for the currentlyused transmission path in the receiving device 10, so that the length ofTc(S) is shorter than the length of Tc(L). In case that are-synchronization of the receiving device 10 is not necessary, Tc(S)can be omitted. The preamble sequence Pc(S) has the function to enablethe estimation of the accurate channel quality information in thechannel estimator 16 of the receiving device 10 as well as therealization of the frame timing in the receiving device 10, andtherefore has the same length as the preamble sequence Pc(L). The lengthof the data parts of the long data frame and the short data frame arethe same.

As stated above, in a long data frame, due to the requirement ofswitching the antenna (or other circuitry) back from the candidatetransmission path to the currently used transmission path and of there-synchronization for the currently used transmission path, Tc(L) isrelatively long as compared to Tc(S), which does not need to enable aswitching of the antenna or other circuitry. Since, as can be seen inFIG. 9, most of the time only the transmission of a short data frame isnecessary instead of the transmission of a long data frame, the overheadof Tc can be reduced dramatically. The preamble sequences of the longdata frame, the short data frame and the beam steering data frame canadvantageously be different from each other in order to facilitate thereceiving device 10 to identify which type of frame is being transmittedand received and in order to enable the receiving device to adjust tothe respective frame length. Further, the various frame types explainedin the first and the second embodiment above can be either transmittedin single carriers or in multiple carriers, such as e. g. in an OFDMsystem.

Generally, the present invention enables the transmission and receptionof signals in a wireless communication system with at least onesteerable narrow beam antenna, whereby the direction of the at least onenarrow beam antenna can be steered with low control overhead and areduced frame length for high data rate wireless communication, bydefining novel frame structures. From a physical layer point of view, ina first embodiment a new frame structure enabling the channel estimationfor the currently used transmission path as well as a candidatetransmission path is suggested, whereas in a second embodiment twodifferent frame types, namely a data frame and a beam steering frame aresuggested. Hereby, the overhead for beam steering can be reduced. Afurther overhead reduction can be achieved by defining two differenttypes of data frames in the second embodiment, namely a long data frameand a short data frame as described above.

1. A method for transmitting signals in a wireless communication system,in which signals are transmitted from a first communication device to asecond communication device, said signals being transmitted inconsecutive frames, each frame having a preamble section includingpreamble information, at least one of said first and said secondcommunication devices having a narrow beam antenna which is configuredto steer an antenna beam to different positions, each of said differentpositions corresponding to one of a number of different transmissionpaths from said first to said second communication device, the methodincluding: transmitting and receiving a first preamble section includingpreamble information enabling the estimation of a channel quality of acurrent transmission path, while said antenna beam is in a currentposition corresponding to said current transmission path; steering saidantenna beam from said current position to a different positioncorresponding to a candidate transmission path; and transmitting andreceiving a second preamble section including preamble informationenabling the estimation of a channel quality of said candidatetransmission path while said antenna beam is in said different position,wherein said first and said second preamble section are transmitted indifferent frames, and the number of transmitted frames including asecond preamble section in relation to the number of transmitted framesincluding a first preamble section is varied depending on a detectedmovement information in relation to the first and/or the secondcommunication device.
 2. A method according to claim 1, wherein aftereach frame including a second preamble section a frame including a firstpreamble section with a longer length as compared to the normallytransmitted frames including a first preamble section is transmitted. 3.A method according to claim 1, wherein the first and second preamblesections are different from each other.
 4. A transmission deviceconfigured to transmit signals in a wireless communication system,wherein said signals are transmitted in consecutive frames, each framehaving a preamble section with preamble information, comprising: anarrow beam antenna configured to steer an antenna beam to differentpositions, each of said different positions corresponding to one of anumber of different transmission paths from said transmitting device toa receiving device; a steering unit configured to steer said antennabeam to different positions; a preamble generating unit configured togenerate preamble sections including preamble information; and a controlunit configured to control the transmission of a first preamble sectionincluding preamble information enabling the estimation of a channelquality of a current transmission path while said antenna beam is in acurrent position corresponding to said current transmission path, andfurther configured to control the transmission of a second preamblesection including preamble information enabling the estimation of achannel quality of a candidate transmission path after said antenna beamhas been steered to a different position corresponding to said candidatetransmission path, to control the transmission of signals in which saidfirst and said second preamble section are transmitted in differentframes, and to vary the number of transmitted frames including a secondpreamble section in relation to the number of transmitted framesincluding a first preamble section depending on a detected movementinformation in relation to the transmission and/or receiving device. 5.A transmission device according to claim 4, wherein said control unit isconfigured to control the transmission of signals so that after eachframe including a second preamble section a frame including a firstpreamble section with a longer length as compared to the normallytransmitted frames including a first preamble section is transmitted. 6.A transmission device according to claim 4, wherein the first and secondpreamble sections are different from each other.
 7. A receiving deviceconfigured to receive signals in a wireless communication system,wherein said signals are transmitted and received in consecutive frames,each frame having a preamble section with preamble information,comprising: a narrow beam antenna configured to steer an antenna beam todifferent positions, each of said different positions corresponding toone of a number of different transmission paths from a transmittingdevice to said receiving device; a steering unit configured to steersaid antenna beam to different positions; channel estimation unitconfigured to estimate a channel quality on the basis of receivedpreamble information; and a control unit configured to control thereception of a first preamble section including preamble informationenabling the estimation of a channel quality of a current transmissionpath while said antenna beam is in a current position corresponding tosaid current transmission path, to control the reception of a secondpreamble section including preamble information enabling the estimationof a channel quality of a candidate transmission path after said antennabeam has been steered to a different position corresponding to saidcandidate transmission path to control the reception of signals in whichsaid first and said second preamble section are transmitted in differentframes, and to control the reception of signals in which the number oftransmitted frames including a second preamble section in relation tothe number of transmitted frames including a first preamble section isvaried depending on a detected movement information in relation to thefirst and/or the second communication device.
 8. A receiving deviceaccording to claim 7, wherein said control unit is configured to controlthe reception of signals so that after each frame including a secondpreamble section a frame including a first preamble section with alonger length as compared to the normally transmitted frames including afirst preamble section is received.
 9. A receiving device according toclaim 7, wherein said control unit is configured to control thereception of first and second preamble sections which are different fromeach other.
 10. A method for transmitting signals in a wirelesscommunication system, in which signals are transmitted from a firstcommunication device to a second communication device, said signalsbeing transmitted in consecutive frames, each frame having a preamblesection including preamble information, at least one of said first andsaid second communication devices having a narrow beam antenna which isconfigured to steer an antenna beam to different positions, each of saiddifferent positions corresponding to one of a number of differenttransmission paths from said first to said second communication device,the method comprising: transmitting and receiving a first preamblesection including preamble information enabling the estimation of achannel quality of a current transmission path, while said antenna beamis in a current position corresponding to said current transmissionpath; steering said antenna beam from said current position to adifferent position corresponding to a candidate transmission path; andtransmitting and receiving a second preamble section including preambleinformation enabling the estimation of a channel quality of saidcandidate transmission path while said antenna beam is in said differentposition, wherein said first and said second preamble section aretransmitted in different frames, and after each frame including a secondpreamble section, a frame including a first preamble section with alonger length as compared to the normally transmitted frames including afirst preamble section is transmitted.
 11. A method according to claim10, wherein the number of transmitted frames including a second preamblesection in relation to the number of transmitted frames including afirst preamble section is varied depending on a detected movementinformation in relation to the first and/or the second communicationdevice.
 12. A method according to claim 10, wherein the first and secondpreamble sections are different from each other.
 13. A transmissiondevice configured to transmit signals in a wireless communicationsystem, wherein said signals are transmitted in consecutive frames, eachframe having a preamble section with preamble information, comprising: anarrow beam antenna configured to steer an antenna beam to differentpositions, each of said different positions corresponding to one of anumber of different transmission paths from said transmitting device toa receiving device; a steering unit configured to steer said antennabeam to different positions; a preamble generating unit configured togenerate preamble sections including preamble information; and a controlunit configured to control the transmission of a first preamble sectionincluding preamble information enabling the estimation of a channelquality of a current transmission path while said antenna beam is in acurrent position corresponding to said current transmission path, andfurther configured to control the transmission of a second preamblesection including preamble information enabling the estimation f achannel quality of a candidate transmission path after said antenna beamhas been steered to a different position corresponding to said candidatetransmission path, to control the transmission of signals in which saidfirst and said second preamble section are transmitted in differentframes, and to control the transmission of signals so that after eachframe including a second preamble section a frame including a firstpreamble section with a longer length as compared to the normallytransmitted frames including a first preamble section is transmitted.14. A transmission device according to claim 13, wherein said controlunit is configured to vary the number of transmitted frames including asecond preamble section in relation to the number of transmitted framesincluding a first preamble section depending on a detected movementinformation in relation to the transmission and/or receiving device. 15.A transmission device according to claim 13, wherein the first andsecond preamble sections are different from each other.
 16. A receivingdevice configured to receive signals in a wireless communication system,wherein said signals are transmitted and received in consecutive frames,each frame having a preamble section with preamble information, thereceiving device comprising: a narrow beam antenna configured to steeran antenna beam to different positions, each of said different positionscorresponding to one of a number of different transmission paths from atransmitting device to said receiving device; a steering unit configuredto steer said antenna beam to different positions; a channel estimationunit configured to estimate a channel quality on the basis of receivedpreamble information; and a control unit configured to control thereception of a first preamble section including preamble informationenabling the estimation of a channel quality of a current transmissionpath while said antenna beam is in a current position corresponding tosaid current transmission path, to control the reception of a secondpreamble section including preamble information enabling the estimationof a channel quality of a candidate transmission path after said antennabeam has been steered to a different position corresponding to saidcandidate transmission path to control the reception of signals in whichsaid first and said second preamble section are transmitted in differentframes, and to control the reception of signals so that after each frameincluding a second preamble section a frame including a first preamblesection with a longer length as compared to the normally transmittedframes including a first preamble section is received.
 17. A receivingdevice according to claim 16, wherein said control unit is configured tocontrol the reception of signals in which the number of transmittedframes including a second preamble section in relation to the number oftransmitted frames including a first preamble section is varieddepending on a detected movement information in relation to the firstand/or the second communication device.
 18. A receiving device accordingto claim 16, wherein said control unit is configured to control thereception of first and second preamble sections which are different fromeach other.